Visible-light-responsive photocatalyst powder, and visible-light-responsive photocatalytic material, photocatalytic coating material and photocatalytic product each using the same

ABSTRACT

A visible-light-responsive photocatalyst powder includes a tungsten oxide powder. The tungsten oxide powder has color whose a* is −5 or less, b* is −5 or more, and L* is 50 or more when the color of the powder is expressed by an L*a*b* color system. Further, the tungsten oxide powder has a BET specific surface area in a range of 11 to 820 m 2 /g.

TECHNICAL FIELD

The present invention relates to a visible-light-responsivephotocatalyst powder, and visible-light-responsive photocatalyticmaterial, photocatalytic coating material and photocatalytic producteach using the same.

BACKGROUND ART

As a photocatalytic material used in the application for stain-proofingand deodorization, titanium oxide is known. The photocatalytic materialis used in various fields of interior and exterior building materials,home appliances such as lighting devices, refrigerators,air-conditioners, and toilets. However, titanium oxide cannot exhibitsufficient photocatalytic performance in indoor environments having onlya small amount of ultraviolet rays because titanium oxide is excited byan ultraviolet region. Therefore, research and development have been inprogress for a visible-light-responsive photocatalyst exhibitingphotocatalytic performance even by visible light.

As the visible-light-responsive photocatalyst, tungsten oxide is known.A patent reference 1 describes a photocatalytic material made oftungsten oxide sputter-deposited on a base material, and tungsten oxidehaving a triclinic crystal structure is mainly used. Since the sputterdeposition exposes the base material to high temperature, heatresistance temperature of some base material does not allow theapplication of the sputter deposition. Since the sputter deposition isoften performed in a highly vacuum chamber, its process control iscomplicated, and it not only costs high depending on the shape and sizeof the base material but also has a difficulty in the deposition on awide range such as on building materials. Moreover, though excellent inhydrophilic property, a visible-light-responsive photocatalytic layermade of sputter-deposited tungsten oxide has a problem that itsperformance of decomposing toxic gas such as acetaldehyde is not highenough.

The use of a tungsten oxide powder as a photocatalyst has been alsostudied. The tungsten oxide powder can be mixed with an organic binderto be applied on a base material, which eliminates the need to exposethe base material to high temperature and makes it possible to form acoating film even on a wide range such as on building materials. As amethod of manufacturing the tungsten oxide powder, there has been knowna method of obtaining a tungsten trioxide (WO₃) powder by heatingammonium paratungstate (APT) in the air (see a patent reference 2). Themethod of heating APT in the air provides a triclinic tungsten trioxidepowder whose particle size is about 0.01 μm (BET specific surfacearea=82 m²/g).

The tungsten trioxide (WO₃) powder generated by the heating of APT inthe air needs to have fine particles in order to have improvedphotocatalytic performance. Applying a disintegration process can makethe particle size small to some degree but has a difficulty in realizingthe particle size of 100 nm or less, for instance. Moreover, turning itto fine powder by the use of the disintegration process causes a changein the crystal structure of the tungsten trioxide (WO₃) fine powder dueto a stress by the disintegration process. Since the stress of thedisintegration process causes a defect of the occurrence of there-combination of electrons and holes, it is thought that photocatalyticperformance is deteriorated. The manufacturing method described in thepatent reference 2 has a problem of low manufacturing efficiency of thetungsten trioxide powder since it requires 20 hour or more kneading inorder to stabilize the BET specific surface area.

As a method of efficiently obtaining a fine powder, a patent reference3, for instance, describes a thermal plasma process. A fine powder whoseparticle size is 1 to 200 nm is obtained by the application of thethermal plasma process. The thermal plasma process can efficientlyprovide a fine powder, but even if the tungsten oxide fine powderproduced by the use of the method described in the patent reference 3 isused as a photocatalyst as it is, it is not always possible to obtain asufficient photocatalytic property. It is thought that this is becausethe tungsten oxide fine powder produced by the thermal plasma methoddoes not sometimes have an optimum optical property or crystalstructure.

Tungsten oxide comes in various kinds such as WO₃ (tungsten trioxide),WO₂ (tungsten dioxide), WO, W₂O₃, W₄O₅, and W₄O₁₁. Among them, tungstentrioxide (WO₃) is mainly used as a photocatalytic material because ofits excellent photocatalytic performance and its stability in aroom-temperature atmosphere. However, tungsten trioxide (WO₃) has adisadvantage that its photocatalytic performance is not stable.Moreover, tungsten trioxide (WO₃) cannot exhibit sufficientphotocatalytic performance if its surface area is small.

Patent Reference 1: JP-A 2001-152130 (KOKAI)

Patent Reference 2: JP-A 2002-293544 (KOKAI)

Patent Reference 3: JP-A 2006-102737 (KOKAI)

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide avisible-light-responsive photocatalyst powder excellent inphotocatalytic performance and its reproducibility by improving andstabilizing visible light-exited photocatalytic performance of atungsten oxide powder, and visible-light-responsive photocatalyticmaterial, photocatalytic coating material and photocatalytic producteach using the same.

A visible-light-responsive photocatalyst powder according to an aspectof the present invention includes a tungsten oxide powder, wherein thetungsten oxide powder has color whose a* is −5 or less, b* is −5 ormore, and L* is 50 or more when the color of the powder is expressed byan L*a*b* color system, and has a BET specific surface area in a rangeof 11 to 820 m²/g.

A visible-light-responsive photocatalyst powder according to anothermode of the present invention includes a tungsten oxide powder, whereinthe tungsten oxide powder has color whose a* is −5 or less, b* is −5 ormore, and L* is 50 or more when the color of the powder is expressed byan L*a*b* color system, and an average particle size (D50) by imageanalysis of the tungsten oxide powder falls within a range of 1 to 75nm.

A visible-light-responsive photocatalytic material according to anaspect of the present invention contains the visible-light-responsivephotocatalyst powder according to the aspect of the present invention ina range of not less than 1 mass % nor more than 100 mass %. Avisible-light-responsive photocatalytic coating material according to anaspect of the present invention contains the visible-light-responsivephotocatalytic material according to the aspect of the present inventionin a range of not less than 0.1 masse nor more than 90 mass %. Avisible-light-responsive photocatalytic product according to an aspectof the present invention includes the visible-light-responsivephotocatalytic material according to the aspect of the presentinvention, or a coating layer of the visible-light-responsivephotocatalytic coating material according to the aspect of the presentinvention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a chart showing the result of X-ray diffraction of a tungstenoxide powder according to an example 1.

FIG. 2 is a chart showing the result of X-ray diffraction of a tungstenoxide powder according to a comparative example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment for carrying out the present invention willbe described. A visible-light-responsive photocatalyst powder accordingto the embodiment of the present invention includes a tungsten oxidepowder. The tungsten oxide powder composed of thevisible-light-responsive photocatalyst powder has color whose a* is −5or less, b* is −5 or more, and L* is 50 or more when the color of thepowder is expressed by an L*a*b* color system (L-star/a-star/b-starcolor system), and has a BEt specific surface area in a range of 11 to820 m²/g. Alternatively, the tungsten oxide powder has color whose a* is−5 or less, b* is −5 or more, and L* is 50 or more when the color of thepowder is expressed by the L*a*b* color system (L-star/a-star/b-starcolor system), and an average particle size (D50) by image analysis ofthe tungsten oxide powder falls within a range of 1 to 75 nm.

The L*a*b* color system is a method used to express color of an objectand is standardized by Commission Intanationale del'Eclairage (CIE) in1976, and its definition is in JIS Z-8729 in Japan. L* expresseslightness and a* and b* express hue and saturation. The larger *L is,the higher lightness is expressed. a* and b* express the directions ofcolor, a* expressing a red direction, −a* expressing a green direction,b* expressing a yellow direction, and −b* expressing a blue direction.Saturation is expressed by (c*)=((a*)²+(b*)²)^(1/2).

The tungsten oxide powder of this embodiment has the color whose a* is−5 or less, b* is −5 or more, and L* is 50 or more. This indicates thatthe tungsten oxide powder has a hue from yellow to the vicinity of greenand has high saturation and lightness. When it has such an opticalproperty, its photocatalytic performance by visible light excitation canbe improved. The color tone of the tungsten oxide powder is thought tochange based on composition fluctuation due to oxygen deficiency, lightirradiation, and so on, and when it has the above-described hue,saturation, and lightness, good photocatalytic performance can beobtained.

When it has a hue close to blue, it is thought that there is a highdegree of oxygen deficiency or the like, and the tungsten oxide powderhaving such a hue cannot exhibit sufficient photocatalytic performance.That is, when a* is over −5 or b* is less than −5, sufficientphotocatalytic performance cannot be obtained. It is thought that thisis because there occurs a fluctuation in the composition of tungstenoxide (WO₃) due to the oxygen deficiency and the like. Similarly, whenL* is less than 50, sufficient photocatalytic performance cannot beobtained either.

Therefore, when a* and b* expressing the hue of the tungsten oxidepowder are −5 or less and −5 or more respectively and L* expressing itslightness is 50 or more, it is possible to obtain good photocatalyticperformance with high reproducibility. The tungsten oxide powderpreferably has color whose a* is −8 or less, b* is 3 or more, and L* is65 or more, and in such a case, the photocatalytic performance furtherimproves. Desirably, a* is in a range of −20 to −10, b* is in a range of5 to 35, and L* is 80 or more.

The photocatalytic performance of the tungsten oxide powder can beenhanced not only by the aforesaid color tone (a*≦−5, b*≧−5, L*≧50).Specifically, when the tungsten oxide powder satisfying the powder colorexpressed by the L*a*b* color system and having the BET specific surfacearea in the range of 11 to 820 m²/g is used as thevisible-light-responsive photocatalyst powder, it is possible to stablyobtain excellent photocatalytic performance. Assuming that a specificgravity of tungsten oxide is 7.3, an average particle size convertedfrom the BET specific surface area falls within a range of 1 to 75 nm.

When the tungsten oxide powder satisfying the powder color expressed bythe L*a*b* color system and having the average particle size in therange of 1 to 75 nm is used as the visible-light-responsivephotocatalyst powder, it is possible to stably obtain excellentphotocatalytic performance. It is assumed that the average particle sizeis calculated based on an average particle size of particles in numbern=50 (D50) by image analysis of a photograph of SEM, TEM, or the like.The average particle size (D50) may be equal to the average particlesize converted from the specific surface area.

The larger the specific surface area and the smaller the particle size,the higher the performance of the photocatalyst powder. Therefore, whenthe BET specific surface area is less than 11 m²/g (the average particlesize is over 75 nm), sufficient photocatalytic performance cannot beobtained even when the tungsten oxide powder satisfies the aforesaidcolor tone. When the BET specific surface area of tungsten oxide is over820 m²/g (the average particle size is less than 1 nm), practicabilityis lowered because handlability as powder deteriorates.

The BET specific surface area of the tungsten oxide powder preferablyfalls within a range of 20 to 820 m²/g, and more preferably, within arange of 55 to 250 m²/g. The average particle size (D50) by imageanalysis preferably falls within a range of 1 to 41 nm, and morepreferably, within a range of 3.3 to 15 nm. In order to enhancephotocatalytic performance of the tungsten oxide powder, the larger thespecific surface area and the smaller the average particle size, thebetter, but if the particle size of the tungsten oxide powder is toosmall, dispersibility of the particles lowers, which makes it difficultto turn it to a coating material, and therefore, care should be takenfor a dispersion method.

The visible-light responsive photocatalyst powder includes the tungstenoxide powder having the color tone (a*≦−5, b*≧−5, L*≧50) expressed bythe L*a*b* color system, and the BET specific surface area in the rangeof 11 to 820 m²/g and/or the average particle size (D5) in the range of1 to 75 nm. Using the tungsten oxide powder satisfying such conditionsmakes it possible to provide a visible-light-responsive photocatalystpowder whose photocatalytic performance by visible light excitation isimproved.

The tungsten oxide powder composed of the visible-light-responsivephotocatalyst powder preferably has a crystal structure made of a mixedcrystal of at least one or two or more selected from a monocliniccrystal, a triclinic crystal, and a rhombic crystal. The tungsten oxidepowder having such a crystal structure, when used, can stably exhibitexcellent photocatalytic performance. The crystal structure of thetungsten oxide powder is determined by X-Ray diffraction, and generally,several peaks exist in 22.5 to 25° of 2θ range. When the particle sizeis small, the peaks in the X-ray diffraction become broad and aredifficult to separate. FIG. 1 shows the result of the X-diffraction of atungsten oxide powder of a later-described example 1.

As is apparent from FIG. 1, it is recognized that peaks exist in 22.5 to25° of 2θ range, but the peaks are not clearly separated. Though peaksexist also in 33 to 35° of 2θ range, they are broad. Though it isdifficult to clearly determine the crystal structure of a tungsten oxidepowder having a small particle size by the X-ray diffraction, when thereexists the highest peak in 22.5 to 25° of 2θ range and there exist peaksin 33 to 35° of 2θ range, the tungsten oxide powder can stably exhibitgood photocatalytic performance.

In tungsten oxide, crystal systems such as the monoclinic, rhombic,triclinic, and cubic systems, and so on exist, and they do notnecessarily exist alone. When crystal systems having similar peakpatterns exist together, the peaks become broad and are difficult toseparate. When the particle size of the tungsten oxide powder is smalland in addition when crystal systems having similar peak patterns existtogether, the peaks also become broad and they are difficult toseparate. When the highest peak is in 22.5 to 25° of 2θ range and thepeaks exist in 33 to 35° of 2θ range, it can be inferred that tungstenoxide is mainly made of one kind or two kinds or more selected from themonoclinic, triclinic, and rhombic crystals.

The tungsten oxide powder composed of the photocatalyst powder ispreferably made mainly of WO₃ (tungsten trioxide). Desirably, thetungsten oxide powder is substantially made of WO₄, but may containanother kind of oxide (WO₂, WO, W₂O₃, W₄O₅, W₄O₁₁, or the like). Thetungsten oxide powder may be substantially made of WO₃, or may be amixture of WO₃ as the main component and another oxide (WO_(x)), butpreferably satisfies the crystal structure based on the aforesaid peakcondition of the result of the X-ray diffraction.

The tungsten oxide powder composed of the visible-light-responsivephotocatalyst powder may contain a trace amount of a metal element asimpurities. The content of the metal element as the impurity element ispreferably 10 mass % or less. In order to suppress a change in the colortone of the tungsten oxide powder, the content of the impurity metalelement is desirably 2 mass % or less. Examples of the impurity metalelement are an element normally contained in a tungsten mineral and acontaminant element which is mixed when a tungsten compound or the likeused as a raw material is produced. Concrete examples of the impuritymetal element are Fe, Mo, Mn, Cu, Ti, Al, Ca, Ni, Cr, Mg, and the like.

The nitrogen content of the tungsten oxide powder composed of thevisible-light-responsive photocatalyst powder is preferably 300 ppm orless (mass ratio). The smaller an amount of the impurities in thetungsten oxide powder, the better. In particular, since nitrogen is afactor causing the deterioration in crystallinity of the tungsten oxidepowder, its content is preferably 300 ppm or less. It is thought that,when the nitrogen content is 300 ppm or less, crystallinity improves,which makes it difficult for the re-combination of electrons and holesto occur. The nitrogen content of the tungsten oxide powder is morepreferably 150 ppm or less.

Since the visible-light-responsive photocatalyst powder of thisembodiment has a large specific surface area (small average particlesize) and in addition uses the tungsten oxide powder whose tone of thepowder color is made appropriate, it is possible to improve andstabilize the photocatalytic performance by visible light excitation.Moreover, controlling the crystal structure and an amount of an impurityelement such as nitrogen of the tungsten oxide powder enables furtherimprovement in the photocatalytic performance. Further, the tungstenoxide powder of this embodiment is excellent in dispersibility since itszeta potential in a pH 1 to 7 aqueous solution is minus, and thus can beapplied on a base material thinly and evenly.

Examples of the photocatalytic performance are performance ofdecomposing organic gas such as acetaldehyde and formaldehyde, ahydrophilic property, antibacterial performance, and disinfectionperformance. Here, visible light is light in a 390 to 830 nm wavelengthrange. The tungsten oxide powder of this embodiment has excellentphotocatalytic performance when irradiated with 430 to 500 nm light.Examples of an excitation source emitting light with a 430 to 500 nmwavelength are sunlight, a fluorescent lamp, a blue-emitting diode, ablue laser, and the like. In particular, the blue-emitting diode and theblue laser are preferable since they can emit only light with a 430 to500 nm wavelength.

The tungsten oxide powder composed of the visible-light-responsivephotocatalyst powder of the above-described embodiment is manufacturedas follows, for instance. The tungsten oxide powder is manufactured bythe use of a sublimation process. Combining a heat treatment processwith the sublimation process is also effective. According to thetungsten trioxide powder manufactured by the use of the sublimationprocess or the combination of the sublimation process and the heattreatment process, it is possible to stably realize the aforesaid colortone and BET specific surface area. Further, when the powder isevaluated by SEM or TEM, the average particle size of primary particlesapproximates a value converted from the BET specific surface area, andit is possible to stably provide a powder small in particle sizevariation.

First, the sublimation process will be described. The sublimationprocess is a process to obtain a tungsten oxide powder by sublimating ametal tungsten powder, a tungsten compound powder, or a tungstencompound solution in an oxygen atmosphere. Sublimation is a phenomenonin which a state change from a solid phase to a vapor phase or from avapor phase to a solid phase occurs not through a liquid phase. Byoxidizing the metal tungsten powder, the tungsten compound powder, orthe tungsten compound solution as a raw material while sublimating it,it is possible to obtain a tungsten oxide powder in a fine powder state.

As the raw material of the sublimation process (tungsten raw material),any of the metal tungsten powder, the tungsten compound powder, and thetungsten compound solution may be used. Examples of the tungstencompound used as the raw material are tungsten trioxide (WO₃), tungstendioxide (WO₂), tungsten oxide such as low-grade oxide, tungsten carbide,ammonium tungstate, calcium tungstate, tungstic acid, and the like.

By the sublimation process of the above-described tungsten raw materialin the oxygen atmosphere, the metal tungsten powder or the tungstencompound powder is instantaneously changed from a solid phase to a vaporphase, and oxidizing metal tungsten vapor changed to the vapor phaseresults in a tungsten oxide powder. When a solution is used, it alsochanges to a vapor phase through a tungsten oxide or compound. By thususing an oxidation reaction in the vapor phase, it is possible to obtaina tungsten oxide fine powder. Further, the color tone and crystalstructure of the tungsten oxide fine powder can be controlled.

As the raw material of the sublimation process, it is preferable to useat least one kind selected from a metal tungsten powder, a tungstenoxide powder, a tungsten carbide powder, and an ammonium tungstatepowder since the tungsten oxide powder obtained by the sublimation inthe oxygen atmosphere is less likely to contain impurities. The metaltungsten powder and the tungsten oxide powder are especially preferableas the raw material of the sublimation process since they do not containa toxic substance as a byproduct (substance other than tungsten oxide)produced in the sublimation.

As the tungsten compound used as the raw material, a compound containingtungsten (W) and oxygen (O) as its constituent elements is preferable.The tungsten compound containing W and O as its components is easilysublimated instantaneously when a later-described inductively-coupledplasma process is applied in the sublimation process. Examples of such atungsten compound are WO₃, W₂₀O₅₈, W₁₈O₄₉, WO₂, and the like. Solutions,salts, or the like of tungstic acid, ammonium paratungstate, ammoniummetatungstate are also effective.

The metal tungsten powder or the tungsten compound powder as thetungsten raw material preferably has an average particle size in a rangeof 0.1 to 100 μm. The average particle size of the tungsten raw materialmore preferably falls within a range of 0.3 μm to 10 μm, still morepreferably, within a range of 0.3 μm to 3 μm, and desirably within arange of 0.3 μm to 1.5 μm. When the metal tungsten powder or thetungsten compound powder having the average particle size in the aboverange is used, the sublimation easily occurs.

When the average particle size of the tungsten raw material is less than0.1 μm, the powder of the raw material is too fine, and thus advanceadjustment of the raw material powder is required and handlability islowered, and in addition, high cost is required, which is notindustrially preferable. When the average particle size of the tungstenraw material is over 100 μm, a uniform sublimation reaction is difficultto occur. Even if the average particle size is large, processing with alarge energy amount can cause a uniform sublimation reaction, but thisis not industrially preferable.

As a method of sublimating the tungsten raw material in the oxygenatmosphere in the sublimation process, at least one process selectedfrom an inductively-coupled plasma process, an arc discharge process, alaser process, an electron beam process, and a gas burner process ispossible. In the laser process and the electron beam process, thesublimation process is performed by the irradiation of a laser beam oran electron beam. Since the laser beam and the electron beam each have asmall irradiation spot diameter, they need a long time to process alarge amount of the raw material at a time, but have an advantage thatthere is no need to strictly control the particle size of the rawmaterial powder and stability of its supply amount.

The inductively-coupled plasma process and the arc discharge process cancause an oxidation reaction of a large amount of the raw material powderat a time in an oxygen atmosphere though requiring the adjustment of ageneration area of plasma or arc discharge. Moreover, an amount of theraw material processable at a time can be controlled. The gas burnerprocess has a difficulty in processing a large amount of the rawmaterial powder or the raw material solution though requiring a smallmotive power expense. Therefore, the gas burner process is inferior inproductivity. A gas burner may be any having an energy high enough tocause the sublimation, and is not particularly limited. A propane gasburner, an acetylene gas burner, or the like is used.

When the inductively-coupled plasma process is applied to thesublimation process, a generally used method is a method in which plasmais generated by using argon gas or oxygen gas and a metal tungstenpowder or a tungsten compound powder is supplied to the plasma. A methodof supplying the tungsten raw material into the plasma is, for example,a method of injecting a metal tungsten powder or a tungsten compoundpowder together with carrier gas, a method of injecting a dispersionliquid in which the metal tungsten powder or the tungsten compoundpowder is dispersed in a predetermined liquid dispersion medium, or thelike.

The carrier gas used when the metal tungsten powder or the tungstencompound powder is injected into the plasma is, for example, air,oxygen, inert gas containing oxygen, or the like. Among them, air ispreferably used because of its low cost. When a reaction field containsa sufficient amount of oxygen such as a case where reaction gascontaining oxygen is injected besides the carrier gas or a case wherethe tungsten compound powder is tungsten trioxide, inert gas such asargon or helium may be used as the carrier gas. As the reaction gas, theuse of oxygen or inert gas containing oxygen is preferable. When theinert gas containing oxygen is used, an oxygen amount is preferably setso that a sufficient amount of oxygen necessary for the oxidationreaction can be supplied.

Applying the method of injecting the metal tungsten powder or thetungsten compound powder with the carrier gas and adjusting a gas flowrate and the pressure in a reaction vessel facilitate the control of thecolor tone and crystal structure of the tungsten trioxide powder.Concretely, it is easy to obtain a tungsten trioxide powder having theaforesaid color tone expressed by the L*a*b* color system and theaforesaid crystal structure made of the mixed crystal of one kind or twokinds or more selected from the monoclinic crystal, the tricliniccrystal, and the rhombic crystal. In order to simultaneously control thespecific surface area (particle size) and the color tone of the tungstentrioxide powder, it is necessary to adjust the power of the plasma, thekind of gas, gas balance, the gas flow rate, the pressure in thereaction vessel, a supply amount of the raw material powder, and so on.Each of these values cannot be decided to a single value because theproperty varies depending on how these parameters are combined.

The dispersion medium used in the preparation of the dispersion liquidof the metal tungsten powder or the tungsten compound powder is a liquiddispersion medium having oxygen atoms in its molecules, or the like.Using the dispersion liquid facilitates handling of the raw materialpowder. As the liquid dispersion medium having oxygen atoms in itsmolecules, that containing 20 vol. % or more of at least one kindselected from water and alcohol is used, for instance. As alcohol usedas the liquid dispersion medium, at least one kind selected frommethanol, ethanol, 1-propanol, and 2-propanol is preferable, forinstance. Water and alcohol do not obstruct the sublimation reaction andthe oxidation reaction of the raw material powder because of their easyvolatility by heat of plasma, and easily promote the oxidation reactionbecause they contain oxygen in its molecules.

When the dispersion liquid is prepared by dispersing the metal tungstenpowder or the tungsten compound powder in the dispersion medium, it ispreferable that the dispersion liquid contains the metal tungsten powderor the tungsten compound powder in a range of 10 to 95 mass %, and morepreferably, in a range of 40 to 80 mass %. By setting the dispersionamount in the dispersion liquid to such a range, it is possible touniformly disperse the metal tungsten powder or the tungsten compoundpowder in the dispersion liquid. The uniform dispersion facilitates theuniform occurrence of the sublimation reaction of the raw materialpowder. If the content in the dispersion liquid is less than 10 mass %,an amount of the raw material powder is too small and efficientmanufacture is not possible. If the content is over 95 mass %, the rawmaterial powder has an increased viscosity due to a small amount of thedispersion liquid and thus easily sticks to the vessel, which lowershandlability.

Applying the method of dispersing the metal tungsten powder or thetungsten compound powder in the dispersion liquid and injecting thedispersion liquid into the plasma facilitates controlling the color toneand crystal structure of the tungsten trioxide powder. Further, usingthe tungsten compound solution as the raw material also enables auniform sublimation reaction and improves controllability of the colortone and crystal structure of the tungsten trioxide powder. The methodof using the dispersion liquid is also applicable to the arc dischargeprocess.

When the sublimation process is performed by the irradiation of a laserbeam or an electron beam, it is preferable to use the metal tungsten orthe tungsten compound in a pellet form as the raw material. Since thelaser beam and the electron beam each have a small irradiation spotdiameter, the use of the metal tungsten powder or the tungsten compoundpowder makes the supply difficult, but using the metal tungsten ortungsten compound in a pellet form enables efficient sublimation. Thelaser may be any having an energy high enough to sublimate the metaltungsten or the tungsten compound and is not particularly limited, but aCO₂ laser is preferable because of its high energy.

When the pellet is irradiated with the laser beam or the electron beam,moving at least one of an irradiation source of the laser beam or theelectron beam and the pellet enables effective sublimation of the wholesurface of the pellet having a certain degree of size. This makes iteasy to obtain the tungsten trioxide powder having the predeterminedcolor tone and crystal structure. The pellet of the metal tungsten orthe tungsten compound is also applicable to the inductively-inducedplasma process and the arc discharge process.

In order to simultaneously control the specific surface area (particlesize) and the color tone of the tungsten trioxide powder, it isnecessary to adjust the power of the laser beam or the electron beam,the kind of atmosphere gas, gas balance, the gas flow rate, the pressurein the reaction vessel, the density of the pellet, a moving speed of anirradiation spot, and so on. Each of these values cannot be decided to asingle value because the property varies depending on how theseparameters are combined. When the gas burner process is applied, it isalso necessary to adjust the power of a gas burner, the kind ofatmosphere gas, gas balance, the gas flow rate, the pressure in thereaction vessel, a feeding speed of the raw material, and so on. Each ofthese values cannot be decided to a single value because the propertyvaries depending on how these parameters are combined.

The tungsten oxide powder composed of the visible-light-responsivephotocatalyst powder of this embodiment can be obtained only by thesublimation process, but it is also effective to subject the tungstenoxide powder produced by the sublimation process to a heat treatmentprocess. In the heat treatment process, the tungsten trioxide powderobtained by the sublimation process is heat-treated in an oxideatmosphere at a predetermined temperature and for a predetermined time.Even when a sufficient amount of the tungsten trioxide fine powdercannot be formed by controlling the conditions of the sublimationprocess, performing the heat treatment makes it possible to make a ratioof the tungsten trioxide fine powder in the tungsten oxide powder 99% ormore, or practically 100%. Further, the heat treatment process canadjust the color tone and the crystal structure of the tungsten trioxidefine powder to predetermined states.

Examples of the oxide atmosphere used in the heat treatment are air andoxygen-containing gas. The oxygen-containing gas means inert gascontaining oxygen. The heat treatment temperature preferably fallswithin a range of 300 to 1000° C., and more preferably, within a rangeof 500 to 700° C. The heat treatment time is preferably 10 minutes totwo hours, and more preferably 30 minutes to 1.5 hours. Making thetemperature and the time of the heat treatment process fall within theaforesaid ranges facilitates forming tungsten trioxide from tungstenoxide except tungsten trioxide.

When the heat treatment temperature is lower than 300°, there is apossibility that it is not possible to obtain a sufficient oxidationeffect for turning the powder, which has not been turned into tungstentrioxide in the sublimation process, into tungsten trioxide. When theheat treatment temperature is higher than 1000° C., the tungsten oxidefine particles rapidly grow and accordingly the specific surface area ofthe resultant tungsten oxide fine powder is likely to decrease. Further,by performing the heat treatment process at the aforesaid temperatureand for the aforesaid time, it is possible to adjust the color tone andthe crystal structure of the tungsten trioxide fine powder.

In order to improve photocatalytic performance and a product property,for example, gas decomposition performance and antibacterialperformance, the tungsten oxide powder may contain a transition metalelement. The content of the transition metal element is preferably 50mass % or less. When the content of the transition metal element is over50 mass %, the property as the visible-light-responsive photocatalystpowder may possibly deteriorate. The content of the transition metalelement is preferably 10 mass % or less, and more preferably 2 mass % orless.

The transition metal element is any of elements whose atomic numbers are21 to 29, 39 to 47, 57 to 79, and 89 to 109 respectively. Among them,the use of at least one kind selected from Ti, Fe, Cu, Zr, Ag, and Pt ispreferable. The transition metal element may be mixed with the tungstenoxide powder, or the transition metal element may carry the tungstenoxide powder. The transition metal element with tungsten may form acompound.

The visible-light-responsive photocatalyst powder of this embodiment isusable as a visible-light-responsive photocatalyst as it is.Alternatively, a powder (or substance in a form other than powder)obtained by mixing the visible-light-responsive photocatalyst powderwith another material or by having the other material carry it, or byimpregnating the other material with it can be used as thevisible-light-responsive photocatalyst. A visible-light-responsivephotocatalytic material of this embodiment contains thevisible-light-responsive photocatalyst powder in a range of 1 to 100mass %.

The content of the photocatalyst powder in the visible-light-responsivephotocatalytic material is appropriately selected according to a desiredproperty, but if it is less than 1 mass %, sufficient photocatalyticperformance cannot be obtained. The visible-light-responsivephotocatalyst powder (tungsten oxide powder) may be mixed with particlesof SiO₂, ZrO₂, Al₂O₃, TiO₂, or the like, for instance, or may be carriedby these particles. Further, zeolite or the like may be impregnated withtungsten oxide.

The visible-light-responsive-photocatalyst powder of this embodimentmixed with a solvent, an additive, or the like is used as avisible-light-responsive photocatalytic coating material. As a maincomponent of the photocatalytic coating material, the above-describedvisible-light-responsive photocatalytic material may be used instead ofthe visible-light-responsive photocatalyst powder. The content of thephotocatalyst powder or the photocatalytic material in thevisible-light-responsive photocatalytic coating material is set so as tofall within a range of 0.1 to 90 mass %. When the content of thephotocatalyst powder or the photocatalytic material is less than 0.1mass %, sufficient photocatalytic performance cannot be obtained, andwhen it is over 90 mass %, the property as the coating material lowers.

The solvent or the additive blended in the visible-light-responsivephotocatalytic coating material is water, alcohol, a dispersing agent, abinder, or the like. The binder may be any of an inorganic binder, anorganic binder, and an organic-inorganic complex binder. The inorganicbinder is, for example, colloidal silica, alumina sol, zirconia sol, orthe like. The organic-inorganic complex binder means an organic mattercontaining a metal element such as Si as its component. As an organiccomponent of the organic binder or the organic-inorganic complex binder,silicone resin or the like is used.

The visible-light-responsive photocatalytic coating material is used invarious kinds of products. Concrete examples of thevisible-light-responsive photocatalytic coating material include variouskinds of glass coating agents such as a coating agent for automobileglass and a coating agent for bathroom glass, a bathroom coating agent,coating agents for toilet and wash room, an interior coating material,an electric appliance coating material, and the like. Besides, thephotocatalytic coating material is also effective for various kinds ofproducts requiring gas decomposition performance, antibacterialperformance, and the like.

A visible-light-responsive photocatalytic product according to anembodiment of the present invention includes thevisible-light-responsive photocatalyst powder or photocatalytic materialdescribed above. Alternatively, the photocatalytic product includes acoating layer of the photocatalytic coating material. The photocatalyticproduct is, for example, a product in which the photocatalyst powder orthe photocatalytic material is made to adhere to a base material or thebase material is impregnated therewith or a product in which thephotocatalytic coating material is applied on the base material. Thephotocatalytic products include products containing zeolite, activatedcarbon, porous ceramics, or the like impregnated with the photocatalystpowder.

Concrete examples of the visible-light-responsive photocatalytic productinclude an air-conditioner, an air cleaner, an electric fan, arefrigerator, a microwave oven, a dish washer/drier, a rice cooker, apot, an IH heater, a washing machine, a vacuum cleaner, a lightingfixture (lamp, fixture main body, shade, or the like) sanitary goods, alavatory bowl, a wash basin, a mirror, a bathroom (wall, ceiling, floor,and so on), building materials (indoor wall, ceiling material, floor,exterior wall), interior goods (curtain, carpet, table, chair, sofa,shelf, bed, bedding, and the like), glass, metal sash window, handrail,door, knob, clothes, filter used in home electric appliances, and thelike.

Examples of the base material of the visible-light-responsivephotocatalytic product are glass, plastic, resin such as acryl, paper,fiber, metal, and wood. In particular, when the photocatalytic coatingmaterial is applied on glass, highly transparent glass whose lighttransmittance for light with 550 nm of wavelength is 50%, or more isobtained. The reason for selecting the light with 550 nm of wavelengthis that it is not absorbed by the tungsten oxide powder much and thuslight transmittance of the photocatalytic coating layer itself can bemeasured.

The visible-light-responsive photocatalytic product according to thisembodiment can be used as parts used in living space and in indoor spaceof automobiles. In particular, since automobiles use glass transmittingalmost no ultraviolet, by using the visible-light-responsivephotocatalytic product, it exhibits an effect for organic gasdecomposition, hydrophilic property, stain-proofing, and so on in aspace almost free from ultraviolet. The photocatalyst powder and thephotocatalytic material are effectively used for a deodorizingantibacterial sheet, a shading cover, and the like for automobiles.Further, a coating layer of the photocatalyst powder or thephotocatalytic material is also effective for bathroom glass, watertanks, vases, and so on.

Next, concrete examples of the visible-light-responsive photocatalyticproduct will be described. A cooking device (microwave oven or the like)includes a housing part provided inside a cabinet and a door provided ona front surface of the housing part. The housing part and the door forma heating chamber. On an inner surface side of the door, an innerbarrier made of transparent glass is provided. The coating layer of thevisible-light-responsive photocatalyst powder or photocatalytic materialis provided on at least part of the heating chamber including an innersurface of the inner barrier (inner side of the heating chamber). Thecoating layer of the photocatalyst powder or the photocatalytic materialexhibits the effect of deodorization, bacteria decomposition, and so onwhen irradiated with light of an inner lamp.

In a refrigerator, the visible-light-responsive photocatalyst powder orphotocatalytic material is provided on at least part of members used ina storage chamber, such as a storage chamber inner wall, shelves, awater feed tank, an ice storage box. For example, in a case of arefrigerator including an auto icemaker, a water feed tank is made oftransparent or translucent synthetic resin. The coating layer of thephotocatalyst powder or the photocatalytic material is provided on aninner surface of the water feed tank. The coating layer of thephotocatalyst powder or the photocatalytic material exhibits the effectof disinfecting a surface of the water feed tank, decomposing an organiccompound in ice making water in the tank to purify water quality, andthe like when irradiated with light of an inner lamp. Consequently,tasty ice free from smell can be made.

In an air-conditioner, the visible-light-responsive photocatalyst powderor photocatalytic material is used on at least part of a fin, a filter(especially, a filter for air-conditioner including a light source), anexterior material, and so on. For example, the coating layer of thephotocatalyst powder or the photocatalytic material is provided on asurface of the fin, the filter, the exterior material, or the like. Thecoating layer of the photocatalyst powder or the photocatalytic materialis excited by sunlight or visible light emitted from a light source toexhibit the effect of decomposing and removing a contaminant substancesuch as oil and smell adhering to the air-conditioner.

In an air cleaner and a dehumidifier, the visible-light-responsivephotocatalyst powder or photocatalytic material is used on at least partof a filter (especially, a filter including a light source), an exteriormaterial, and so on. For example, the coating layer of the photocatalystpowder or the photocatalytic material is provided on a surface of thefilter or the exterior material. The coating layer of the photocatalystpowder or the photocatalytic material is excited by sunlight or visiblelight emitted from a light source to exhibit the effect of decomposingand removing a contaminant substance such as oil and smell adhering tothe air cleaner or the dehumidifier. In an electric fan, the coatinglayer of the visible-light-responsive photocatalyst powder or thephotocatalytic material is provided on a blade. The coating layer of thephotocatalyst powder or the photocatalytic material exhibits the effectof decomposing and removing a contaminant substance such as oil andsmell adhering to the electric fan.

In a fluorescent lamp and a desk lamp, the visible-light-responsivephotocatalyst powder or photocatalytic material is used on at least partof a shade. For example, the coating layer of the photocatalyst powderor the photocatalytic material is provided on an inner surface or anouter surface of the shade. The coating layer of the photocatalystpowder or the photocatalytic material is excited by visible lightemitted from the fluorescent lamp or the desk lamp to exhibit the effectof decomposing and removing a contaminant substance such as oil andsmell adhering to the fluorescent lamp or the desk lamp. Further, owingto a stain-proofing effect by the photocatalyst powder or thephotocatalytic material, the shade coated with the photocatalyst isdifficult to get dirty and can be kept clean for a long time.

Building materials such as an interior wall material, a ceilingmaterial, a partition, a blind, a paper sliding door, a paper panel dooras the visible-light-responsive photocatalytic products each have thecoating layer of the photocatalyst powder or the photocatalyticmaterial. The coating layer of the photocatalyst powder or thephotocatalytic material is excited by sunlight or visible light emittedfrom various kinds of light sources to exhibit the effect of decomposingand removing a contaminant substance such as oil and smell adhering tothe interior wall material, the ceiling material, the partition, theblind, the paper sliding door, the paper panel door, and so on. Further,owing to a stain-proofing effect of the photocatalyst powder or thephotocatalytic material, the effect that the building materials coatedwith the photocatalyst is difficult to get dirty is exhibited. Thevisible-light-responsive photocatalyst is also effective for slippersand a cabinet for them, a Christmas tree, and the like.

Fiber products using the visible-light-responsive photocatalyst includea curtain, a partition curtain, a uniform, and so on. The coating layerof the photocatalyst powder or the photocatalytic material is providedon surfaces of these fiber products. Alternatively, fiber in which thephotocatalyst powder is mixed is used to make fiber products such as acurtain, a partition curtain, and a uniform. The photocatalyst powder orthe photocatalytic material is excited by sun light or visible lightemitted from various kinds of light sources to exhibit the effect ofdecomposing and removing a contaminant substance such as oil and smelladhering to the fiber products such as the curtain, the partitioncurtain, and the uniform. The visible-light-responsive photocatalyst isalso effective for fiber products other than these.

EXAMPLES

Next, concrete examples of the present invention and the evaluationresults thereof will be described.

Example 1

A tungsten trioxide powder whose average particle size was 0.5 wasprepared as a raw material powder. This raw material powder was sprayedto RF plasma together with carrier gas (Ar), and as reaction gas, oxygenwas supplied at a flow rate of 75 L/min. A tungsten oxide powder wasproduced through a sublimation process in which an oxidation reaction ofthe raw material powder was caused which the raw material powder wasbeing sublimated. The production condition of the powder is shown inTable 1.

Regarding the obtained tungsten oxide powder, the numerical values ofthe L*a*b* color system, a BET specific surface area, an averageparticle size by image analysis of a TEM photo, the nitrogen content,and the content of a metal element were measured. For the L*a*b*measurement, a spectrophotometric colorimeter CM-2500d manufactured byKONICA MINOLTA was used. For measuring the BET specific surface area, aspecific surface area measuring instrument Macsorb1201 manufactured byMOUNTECH Co., Ltd. was used. A pre-process at this time was performed innitrogen under the condition of 200°×20 minutes. For the TEMobservation, H-7100FA manufactured by HITACHI was used, and an enlargedphoto was subjected to image analysis and 50 particles or more wereextracted, and D50 was calculated by finding a volume-based integrateddiameter.

The measurement results of the color by the L*a*b* color system showedthat a* was −10.9, b* was 9.8, and L* was 85.1. The BET specific surfacearea was 117 m²/g and the average particle size (D50) was 7.8 nm. Theaverage particle size (D50) was equivalent to an average particle sizeconverted from the specific surface area. The nitrogen content of thetungsten oxide powder was 20 ppm and the metal content thereof was 10ppm or less.

The obtained tungsten oxide powder was subjected to X-ray diffraction.For the X-ray diffraction, an X-ray diffraction instrument RINT-2000manufactured by Rigaku Corporation was used, and a Cu target, a Nifilter, and a graphite (002) monochromator were used. Measuringconditions were as follows: tube/bulb voltage: 40 kV, tube/bulb current:40 mA, divergent slit: ½°, scattering slit: auto, light-receiving slit:0.15 mm, 2θ range measured: 20 to 70°, scanning speed: 0.5°/min, andsampling width: 0.004°. The result of the X-ray diffraction is shown inTable 1.

As is apparent from FIG. 1, it is seen that peaks are broad and theirseparation is difficult. However, it is seen that the highest peakexists in a 22.5 to 25° 2θ range and peaks exists also in a 33 to 35° 2θrange. From these, it is inferred that the obtained tungsten oxidepowder has the crystal structure made of a mixed crystal of one kind ortwo kinds or more selected from the monoclinic crystal, the tricliniccrystal, and the rhombic crystal.

Next, in order to evaluate photocatalytic performance of the obtainedtungsten oxide powder, acetaldehyde decomposition performance wasmeasured and evaluated. The acetaldehyde gas decomposition performancewas evaluated by using a circulation type instrument as is used in theevaluation of nitrogen oxide removal performance (decompositionperformance) of JIS-R-1701-1 (2004), under the following conditions. Asa gas analyzing apparatus, a multi-gas monitor 1412 manufactured byINOVA was used. The measurement result is shown in Table 2. It wasconfirmed that a gas residual ratio was 10% and thus gas decompositionperformance was high.

In the evaluation of the acetaldehyde gas decomposition performance, aninitial concentration of the acetaldehyde gas was 10 ppm, a gas flowrate was 140 mL/min, and an amount of a sample was 0.2 g. For theadjustment of the sample, it was applied on a 5×10 cm glass plate andwas dried. In a case of a powder sample, it was spread by water to bedried. In a pre-process, 12-hour irradiation of black light wasperformed. As a light source, a fluorescent lamp (FL20SS·W/18manufactured by Toshiba Lighting & Technology Corporation) was used, andwavelengths of 400 nm or lower were cut by an acrylic plate. Illuminancewas 6000 lx. First, a waiting time without any light irradiation wascontinued until there occurred no gas absorption and the condition wasstabilized. After the stabilization, the light irradiation was started.Under such conditions, the light was emitted and the gas concentrationwas measured 15 minutes later for finding the gas residual ratio.However, when the gas concentration was not stabilized even after 15minutes passed, the light irradiation was continued until thestabilization, and the concentration was measured.

Comparative Example 1

A tungsten oxide powder was produced through the same sublimationprocess as that of the example 1 except in that, as reaction gas, argonwas supplied at a flow rate of 80 L/min and air was supplied at a flowrate of 5 L/min, and the pressure in a reaction vessel was adjusted to apressure-reduced side of 30 kPa. The obtained tungsten oxide powder wassubjected to the same measurement and evaluation as those of theexample 1. The production condition of the tungsten oxide powder isshown in Table 1 and the measurement and evaluation results are shown inTable 2. It was confirmed that the tungsten oxide powder of thecomparative example 1 had small b* and L* values and had poor gasdecomposition performance (gas residual ratio) of 85%.

Examples 2, 3

Tungsten oxide powders were produced through the same sublimationprocess as that of the example 1 except in that, as reaction gas, argonwas supplied at a flow rate of 80 L/min and air was supplied at a flowrate of 5 L/min. In the example 2, the tungsten oxide powder washeat-treated in the atmosphere under the condition of 450°×0.25 h. Inthe example 3, the tungsten oxide powder was heat-treated in theatmosphere under the condition of 550°×0.5 h. The obtained tungstenoxide powders were subjected to the same measurement and evaluation asthose of the example 1. The production conditions of the tungsten oxidepowders are shown in Table 1 and the measurement and evaluation resultsare shown in Table 2. It was confirmed that the tungsten oxide powdersof the example 2 and the example 3 both exhibited excellent gasdecomposition performance. The X-ray diffraction resulted in a patternwhose peak separation was difficult similarly to that of the example 1.

Example 4

Here, the same sublimation process as that of the example 1 wasperformed. However, as a raw material injected to plasma, a tungstenoxide powder containing a large amount of impurities such as Fe and Mowas used. The obtained tungsten oxide powder was subjected to the samemeasurement and evaluation as those of the example 1. The productioncondition of the tungsten oxide powder is shown in Table 1 and themeasurement and evaluation results are shown in Table 2. It wasconfirmed that the tungsten oxide powder exhibited good gasdecomposition performance. From this, it has been confirmed that evencontaining a trace amount of a metal element as an impurity causes noproblem. Incidentally, the X-ray diffraction resulted in a pattern whosepeak separation was difficult similarly to that of the example 1.

Example 5

A tungsten oxide powder was produced through the same sublimationprocess as that of the example 1 except in that, as reaction gas, argonwas supplied at a flow rate of 80 L/min, oxygen was supplied at a flowrate of 10 L/min, and nitrogen was supplied at a flow rate of 40 L/min.The tungsten oxide powder thus obtained was subjected to the samemeasurement and evaluation as those of the example 1. The productioncondition of the tungsten oxide powder is shown in Table 1 and themeasurement and evaluation results are shown in Table 2. It wasconfirmed that, though color tone by the L*a*b* color system and a BETspecific surface area satisfied predetermined values, the tungsten oxidepowder had a high nitrogen content of 500 ppm, and accordingly, had poorgas decomposition performance (gas residual ratio) of 52′, which isslightly lower than that of the example 1. Incidentally, the X-raydiffraction resulted in a pattern whose peak separation was difficult asthat of the example 1.

Comparative Example 2

A tungsten oxide powder produced through the same sublimation process asthat of the example 2 was heat-treated in the atmosphere under thecondition of 1100° C.×0.2 h. The tungsten oxide powder thus obtained wassubjected to the same measurement and evaluation as those of theexample 1. The production condition of the tungsten oxide powder isshown in Table 1 and the measurement and evaluation results are shown inTable 2. It was confirmed that the tungsten oxide powder had a small BETspecific surface area of 5 m₂/g and a large average particle size of 198nm, and as a result, gas decomposition performance was low. It isthought that this is because particle growth occurred by thehigh-temperature heat treatment.

Comparative Example 3

The same measurement and evaluation as those of the example 1 wereperformed by using a tungsten oxide powder (manufactured by RareMetallic Co., Ltd.) available on the market as a reagent. Themeasurement and evaluation results are shown in Table 2. The X-raydiffraction result of the tungsten oxide powder of the comparativeexample 3 is shown in FIG. 2. Though the color tone by the L*a*b* colorsystem was satisfied, it was confirmed that the tungsten oxide powderhad a small BET specific surface area of 0.7 m²/g, and as a result, hadlow gas decomposition performance (gas residual ratio) of 97%.

TABLE 1 production condition sublimation process heat treatment processraw temperature material method (° C.) hour (h) Example 1 WO₃ plasma — —Example 2 WO₃ plasma 450  0.25 Example 3 WO₃ plasma 550 0.5 Example 4WO₃ plasma — — Example 5 WO₃ plasma — — comparative WO₃ plasma — —example 1 comparative WO₃ plasma 1100  0.2 example 2 comparative — — — —example 3

TABLE 2 powder property evaluation result BET specific average gasdecomposition L*a*b* surface area particle size N content metalperformance a* b* L* [m²/g] [nm] [ppm] content (residual ratio) [%]Example 1 −10.9 9.8 85.1 117 7.8 20 <10 ppm 10 Example 2 −10.0 19.9 88.590 10.1 80 <10 ppm 16 Example 3 −11.0 21.3 91.1 71 12.0 50 <10 ppm 22Example 4 −10.5 9.4 89.0 102 8.8 30 Fe: 25 ppm 18 Mo: 20 ppm Example 5−8.6 18.0 55.2 65 13.3 500 <10 ppm 52 comparative −5.0 −11.5 35.7 1257.0 150 <10 ppm 85 example 1 comparative −13.5 40.3 80.1 5 198 20 <10ppm 89 example 2 comparative −16.2 48.1 88.8 0.7 1430 <10 <10 ppm 97example 3

Example 6

A copper oxide (CuO) powder at a ratio of 0.5 mass % was mixed in thetungsten oxide powder obtained in the example 1. The tungsten oxidepowder thus obtained was subjected to the same evaluation of gasdecomposition performance as that of the example 1. The gasdecomposition performance (gas residual ratio) was 20% and it wasconfirmed that high performance on the same level as that of the example1 was exhibited. From this, it has been confirmed that even containingan element (may be an oxide) generally added for improved photocatalyticperformance) in an amount exceeding a range of an amount of impuritiescauses no problem.

Example 7

A water-type coating material containing 5 mass % of the tungsten oxidepowder produced in the example 1 and 0.05 mass % of colloidal silica wasprepared. This was applied on glass to be dried, whereby glass having aphotocatalytic coating layer was fabricated. When gas decompositionperformance of this glass was evaluated according to the aforesaidmethod, it was confirmed that it had an excellent gas residual ratio of15%. Next, transmittance of the glass having the photocatalytic coatinglayer when it was irradiated with light with a 550 nm wavelength wasmeasured. For the measurement of the light transmittance, a UV-Visspectrophotometer UV-2550 manufactured by Shimazu Corporation was used.As a result, the light transmittance was 95% when the film thickness was0.25 μm.

Further, when the aforesaid coating material was applied on glass in anindoor space of an automobile, smell of cigarette was reduced and theglass was not easily stained. Incidentally, when a hydrophilic propertyof the glass coated with the coating material was evaluated, a contactangle was 1′ or less and an ultrahigh hydrophilic property wasexhibited. Further, when antibacterial performance was evaluated byusing Staphylococcus aureus, colon bacillus, and mold, it was confirmedthat excellent antibacterial performance was exhibited against any ofthem. The visible-light-responsive photocatalyst powder of the exampleis excellent in acetaldehyde decomposition performance, or thephotocatalytic coating layer has high transmittance and is unlikely tohave a visual problem such as uneven color. Therefore, they are suitablyused for members used in an indoor space of an automobile, buildingmaterials, and so on.

Example 8

A coating material manufactured in the same manner as that of theexample 7 was applied on a surface of a resin member of a refrigerator.This resin member was subjected to the evaluation of acetaldehyde gasdecomposition performance and antibacterial performance. Theacetaldehyde gas decomposition performance was evaluated in the samemanner as that of the example 1. The antibacterial performance wasevaluated by using Staphylococcus aureus. The Staphylococcus aureus wasmade to adhere to a coating surface of the coating material and thecolony count of the Staphylococcus aureus after light irradiation wasmeasured. The resin member according to the example 8 exhibited goodresults, that is, the gas residual ratio was 18% and the colony count ofthe Staphylococcus aureus after 48 hours was 1200. On the other hand, ina resin member coated with a coating material using the tungsten oxidepowder of the comparative example 1, obtained values were 85% for thegas residual ratio and 100000 for the colony count of the Staphylococcusaureus after 48 hours.

With the visible-light-responsive photocatalytic coating materialapplied on at least part of a refrigerator, the photocatalyst is excitedwhen visible light is turned on even if any ultraviolet emitting meanswhich may possibly has an adverse effect on food is not installed, sothat the effects of deodorization, disinfection, stain-proofing, and soon inside the refrigerator are obtained, and gas components such asethylene and acetaldehyde discharged from vegetables and fruitsthemselves and promoting plant growth are decomposed, which enableslong-term preservation of the vegetables and fruits.

Example 9

A coating material manufactured in the same manner as that of theexample 7 was applied on a surface of an interior material (concrete andwood). This interior material was subjected to the evaluation ofacetaldehyde gas decomposition performance and antibacterialperformance. The acetaldehyde gas decomposition performance wasevaluated in the same manner as that of the example 1. As for theantibacterial performance, water containing Staphylococcus aureus wasapplied on a sample and the colony count of the Staphylococcus aureuswas examined 48 hours later. The interior material according to theexample 9 exhibited good results, that is, the gas residual ratio was18% and the colony count of the Staphylococcus aureus after 48 hours was1200. On the other hand, in an interior material coated with a coatingmaterial using the tungsten oxide powder of the comparative example 1,obtained values were 85% for the gas residual ratio and 100000 for thecolony count of the Staphylococcus aureus after 48 hours.

With the visible-light-responsive photocatalytic coating materialapplied on at least part of an interior material, it is possible toobtain the effects of deodorization, disinfection, stain-proofing, andso on inside a room. It has been confirmed that the same effects areexhibited also for an interior material using base materials ofceramics, plastic, rubber, and the like. Further, it has been confirmedthat the same gas decomposition performance and antibacterialperformance are also obtained when the visible-light-responsivephotocatalytic coating material is applied on various kinds of basematerials in other products.

INDUSTRIAL APPLICABILITY

The visible-light-responsive photocatalyst powder according to theaspect of the present invention is excellent in photocatalyticperformance and its stability owing to its color and specific surfacearea. Therefore, applying such a visible-light-responsive photocatalystpowder makes it possible to provide a visible-light-responsivephotocatalytic material, photocatalytic coating material andphotocatalytic product each excellent in photocatalytic performance byvisible light.

1. A visible-light-responsive photocatalyst powder comprising a tungstenoxide powder, wherein the tungsten oxide powder has color whose a* is −5or less, b* is −5 or more, and L* is 50 or more when the color of thepowder is expressed by an L*a*b* color system, and has a BET specificsurface area in a range of 11 to 820 m²/g.
 2. Thevisible-light-responsive photocatalyst powder according to claim 1,wherein an average particle size (D50) by image analysis of the tungstenoxide powder falls within a range of 1 to 75 nm.
 3. Thevisible-light-responsive photocatalyst powder according to claim 1,wherein when the tungsten oxide powder is measured by X-raydiffractometry, the tungsten oxide powder has a highest peak in 22.5 to25° of 2θ range and has a peak in 33 to 35° of 2θ range.
 4. Thevisible-light-responsive photocatalyst powder according to claim 1,wherein the tungsten oxide powder has color whose a*, b*, and L* in theL*a*b* color system are −8 or less, 3 or more, and 65 or morerespectively.
 5. The visible-light-responsive photocatalyst powderaccording to claim 1, wherein the tungsten oxide powder has a BETspecific surface area in a range of 20 to 820 m²/g.
 6. Thevisible-light-responsive photocatalyst powder according to claim 1,wherein the tungsten oxide powder has the average particle size (D50) byimage analysis in a range of 1 to 41 nm.
 7. The visible-light-responsivephotocatalyst powder according to claim 1, wherein a content of a metalelement as an impurity element in the tungsten oxide powder is 10 mass %or less.
 8. The visible-light-responsive photocatalyst powder accordingto claim 1, wherein a nitrogen content in the tungsten oxide powder is300 ppm or less.
 9. The visible-light-responsive photocatalyst powderaccording to claim 1, wherein the tungsten oxide powder contains atransition metal element in a range of 50 mass % or less.
 10. Avisible-light-responsive photocatalyst powder comprising a tungstenoxide powder, wherein the tungsten oxide powder has color whose a* is −5or less, b* is −5 or more, and L* is 50 or more when the color of thepowder is expressed by an L*a*b* color system, and an average particlesize (D50) by image analysis of the tungsten oxide powder falls within arange of 1 to 75 nm.
 11. The visible-light-responsive photocatalystpowder according to claim 10, wherein when the tungsten oxide powder ismeasured by X-ray diffractometry, the tungsten oxide powder has ahighest peak in 22.5 to 25° of 2θ range and has a peak in 33 to 35° of2θ range.
 12. The visible-light-responsive photocatalyst powderaccording to claim 10, wherein a content of a metal element as animpurity element in the tungsten oxide powder is 10 mass % or less. 13.The visible-light-responsive photocatalyst powder according to claim 10,wherein a nitrogen content of the tungsten oxide powder is 300 ppm orless.
 14. The visible-light-responsive photocatalyst powder according toclaim 10, wherein the tungsten oxide powder contains a transition metalelement in a range of 50 mass % or less.
 15. A visible-light-responsivephotocatalytic material containing the visible-light-responsivephotocatalyst powder according to claim 1 in a range of not less than 1mass % nor more than 100 mass %.
 16. A visible-light-responsivephotocatalytic coating material containing the visible-light-responsivephotocatalytic material according to claim 15 in a range of not lessthan 0.1 mass % nor more than 90 mass %.
 17. A visible-light-responsivephotocatalytic product comprising the visible-light-responsivephotocatalytic material according to claim
 15. 18. Thevisible-light-responsive photocatalytic product according to claim 17,wherein the product is fiber or glass containing thevisible-light-responsive photocatalytic material.
 19. Avisible-light-responsive photocatalytic product comprising a coatinglayer of the visible-light-responsive photocatalytic coating materialaccording to claim
 16. 20. The visible-light-responsive photocatalyticproduct according to claim 19, wherein the product is fiber or glasshaving the coating layer of the visible-light-responsive photocatalyticcoating material.
 21. The visible-light-responsive photocatalyticproduct according to claim 20, wherein the glass coated with thevisible-light-responsive photocatalytic coating material has a lighttransmittance of 50% or more for 550 nm of wavelength.
 22. Thevisible-light-responsive photocatalytic product according to claim 19,wherein the product is disposed in an indoor space of an automobile. 23.A visible-light-responsive photocatalytic product comprising thevisible-light-responsive photocatalyst powder according to claim
 10. 24.A visible-light-responsive photocatalytic product comprising a coatinglayer of a photocatalytic coating material containing thevisible-light-responsive photocatalyst powder according to claim 10.